# OliNo

Renewable Energy

## An energy saving doorbell

The energy consumption of an electrical doorbell is very inefficient. It uses energy 24 hours/day while being used only a few seconds per day. In this article, I describe how I reduced the energy consumption of my doorbell.

### My Doorbell System

My doorbell system consists of:

• Three pushbuttons at the door (three, because I have rooms for rent), all these pushbuttons have a small internal lamp for illuminating the nameplate.
• Four bells (one pushbutton is driving two bells).
• One transformer.

For the amount of energy they consume annually, the few seconds of energy used when doorbells are actually in use is negligible. The energy consumption is determined by:

• The energy loss in the transformer.
• The power for the illumination of the pushbuttons.

### The First Transformer

Input voltage: 220 Volt
Output voltage: 8V (1A)

This old transformer is from the time when the wall outlet voltage was 220 Volt here in the Netherlands, nowadays the wall outlet voltage is 230 V.

Transformer 1

### Bigger Transformator

Later I got three pushbuttons at the door, and I started using this larger transformer. The transformer had to be larger because the old transformer didn’t have enough power to drive two bells in parallel.

Input voltage: 230 Volt
Output voltage: 6 Volt (2A)

Though the bells are 8 Volt types, they also work o.k. on 6 Volt. The lamps in the pushbuttons however gives less light at 6V

Transformer 2

### Toroidal Transformer

To reduce the energy consumption, I replaced transformer 2 by this toroidal transformer. Such a toroidal transformer has much less energy losses then the previous two EI-core transformers.

Input voltage: 230 volt
Output voltage: 6 Volt (2.5 A)

More info about power loss in transformers can be found in the article Saving energy with the toroidal transformer.

Toroidal transformer

### The Measurements

In the next measurement the input power is measured for the three transformers. One time unloaded, and one time loaded with the (lamps in the) three pushbuttons.

Input power
(Watt)
Input power
(Watt)
Transformer 1 1.86 2.78
Transformer 2 1.85 2.45
Toroidal transformer < 0.50 * 0.92

* My energy meter cannot measure below 0.50 Watt.

The result: the toroidal transformer uses the least energy.

### LED Lights in the Pushbutton

To reduce the energy consumption even further, I replaced the light bulbs in the pushbuttons with LED’s. The original light bulbs used about  30 mA a piece (at 6.9 Volt transformer voltage). So the total power for the 3 lamps is: 3 lamps x 30 mA x 6.9 Volt = 0.621 Watt.

Left: the original circuit diagram with the light bulb parallel to the switch.
Right: circuit diagram of the led illumination.

I used two white 3 mm led’s , with 2800 mcd brightness at 20 mA. One led illuminates the transparent circle around the pushbutton. The other led illuminates the nameplate. The light bulb is disconnected.

The led’s and resistor build in the pushbutton.

The illumination for one pushbutton now uses 3.8 mA a.c., which is quite less then the 30 mA it was first. Compared to the light bulb, the brightness of the led’s is much higher.

The illumination at night.

### Voltage Spikes

When the bell is ringing, it can produce high voltage spikes, by which the led’s (maybe) can get defective. To prevent this, I connected a 25 Volt a.c. varistor parallel to the bell. The varistor reduces the peaks to about 40 Volt, which is a safe value.
The value of the varistor may lay between 10 and 25 Volt a.c.

The bell with between it’s terminals the varistor (round blue component).

### Significant Energy Saving

After replacing the light bulbs with LED’s, I measured again the energy consumption of the toroidal transformer, loaded with the three pushbuttons. My energy meter indicated 0.00 Watt, which means the consumption is below 0.5 Watt. Then I connected a small load to the energy meter, to overcome the 0.5 Watt measuring threshold. When I also connected the doorbell transformer, the measured power increased by 0.20 Watt, from which I conclude the doorbell system now consumes about 0.2 Watt. First the power consumption was 2.45 Watt, so this is reduced by more then 10 times. The saving is 2.45 – 0.2 = 2.25 Watt. This is a saving of 19.7 kWh per year.

The low power loss of the toroidal transformer can also be noticed when you touch the transformer with your fingers. You don’t feel any heat production, while the old transformers became quite warm.

### 20 Responses to “An energy saving doorbell”

1. Jeanne Eisenhut Says:

Thank you for a very interesting article. However, we use 110 volts here in the U.S. and I wonder how this would correlate in energy savings.

2. Dick Kleijer Says:

Hello Jeanne,

The transformer losses and savings will be comparable for the 230 and 110 volts system.

3. Jeanne Eisenhut Says:

I actually found LED lamp doorbells at Lowe’s Hardware stores and it’s easy to replace the existing doorbells with this type. We have a two-family house, meaning that we rent out part of our home and we use an old Nutone intercom system so that we can speak with visitors at the door without going downstairs to the first level. In this way we can screen out the unwanted solicitors and pollsters who regularly patrol our neighborhood. The doorbell that’s a part of this system recently became defective and it needs to be replaced. It is a doorbell without a lamp in it. It has become quite difficult to find a doorbell without a lamp of any kind already in it. We’ve been told that we’ll have to go to a specialty electrial store to find such a doorbell. I suppose a doorbell without a lamp would be most efficient and then one wouldn’t consume as much energy as with an LED.

4. KuddlKat Says:

Thanks for the paragraph regarding voltage spikes. From my time as an Electronics Technician in the Navy, I was assuming that the coils for the chimes was causing an inductive kick or some kind of spike that was taking out the LEDs in the test rig I set up. I found this site while searching for a solution after losing some really nice blue and purple LEDs.

5. Margaret Says:

Thank you for this information. The 40-year old transformer for my doorbell runs very hot, so I want to replace it. I am also installing a datalogger/temperature display for my solar hot water collector which can take from 5.5-30 VDC. I’m trying to figure out what power supply would be most efficient to install to power both the datalogger and my doorbell. I tested my door chime which is rated at 10 VAC, and it works just fine when I power it with 6 VDC, 7.5 VDC or 9 VDC. Because the toroidal transformer only produces AC output, but I need a DC output for the datalogger, do you have any recommendations? also, when you say the LED can take up to 40 V surge, is that true in general of LEDs? I am wondering how I can limit the spike to 30 VDC max so as to not damage my datalogger.

6. Dick Kleijer Says:

Hello Margaret,

You may use this:
Use a toroidal transformer with two 9 volt output windings.
One is directly used for the doorbell.
The other 9 Volt winding is connected to a rectifier (4 diodes) followed by a 4700 uF / 25V capacitor.
This produces about 13 VDC for the datalogger.
No need to reduce voltage spikes because the circuits are separated.

Led’s only can handle very low voltage spikes, just above the normal working voltage (2 – 3,5 Volt , depending on Led colour).
The rest of the 40 volt is in this case dissipated in the 1 k-Ohm serie-resistor.

7. Margaret Says:

Thanks for the fast and helpful response! It is too bad I can’t find such a toroidal transformer for less than about \$15-20 USD plus shipping. Not sure why it is that I can buy a efficiency level V, 9 VDC transformer brick for my datalogger for \$7, the most efficient transformer brick that is currently available, but can’t find a plain toroidal transformer for less money. (information on the efficiency level ratings for external power supplies is given at http://www.energystar.gov/ia/partners/prod_development/revisions/downloads/International_Efficiency_Marking_Protocol.pdf )

Anyway, thank you for the elegant solution, I just wish it were cheaper! I had initially thought along those lines but my circuitry knowledge is extremely rusty and my friends who are experts in electronics haven’t been very helpful. They think it’s silly that I’m going to so much effort to save a few watts. I may still use the DC brick that goes with the datalogger because it is already efficient and so I won’t have to rig my own DC output from the toroidal transformer.

I still would like to replace the transformer for the door chime, but \$20 seems a little bit much for that.

Unfortunately this DC brick for the datalogger is rated only at 0.15 A, not enough to also power the door chime. I’m not sure but I think I need to allow 0.5 A for the door chime. The transformer I have now says VAC, 5 VA.

8. Margaret Says:

I found a toroidal transformer rated at 230V input, 18V output. If I operate it at 115-120V input, should I expect a proportional output at about 9-9.4V? Any reason not to do that? because I found a great deal on this toroidal transformer rated at 230V.

9. Dick Kleijer Says:

Hello Margaret,

You can indeed use this transformer without problem, and get about 9 V output.
Much succes with it.

10. Where are the Hyper-Watters? | Eric's Blog Says:

[…] Know how much energy your doorbell uses […]

11. What is a Hyper-Watter? | mapawatt Says:

[…] Know how much energy your doorbell uses […]

12. Eric Says:

This is great!

But I found toroidal transformers to be expensive. I read on one solar-related DC wiring site that a standard doorbell will work fine on 12V DC.

I tried it with a 12V DC adapter, and it does work fine. I think I will switch out the current transformer for a high-efficiency 12VDC switching power supply, and it should be a good solution as well!

13. Jeremy Says:

I have a 12 V AC doorbell powered by a rail mounted power supply in the switchboard. This is continually warm. Can anyone recommend a high efficiency, low standby rail mounted 12 V AC power supply? I’m in Australia, so the input is 230 V AC, 50 Hz.

14. Daniel Rigney Says:

Could you hookup a motion sensor to your doorbell system to further improve energy efficiency?

15. Dick Kleijer Says:

@ Daniel,

Maybe the motion sensor consumes more energy then the doorbell system is using now, so I leave it as it is now.
It is energy efficient enough for me now.

16. liv Says:

Considering I’ve only had people use my doorbell a half a dozen times in the last decade or so, if I ever find the transformer…. I think I’ll just disconnect it.

17. Alex Van den Bossche Says:

Indeed, without lamp, we have maybe 0.001 kWh real output on 20 kWh/year:
some 0.005% efficiency. I replaced my transformer by a 5V SMPS (switched mode power supply adapter. They are often at less than 0.3W in stand by now. Even non-rechargeable Li-batteries would be cheaper.

18. TrueHeart Says:

Here in the US, 20kWh cost \$2-4 per year. Statisticly, I’ll save between \$40-80 in my remaining life. This is assuming that I don’t move and the new parts last that long.

The conversion will cost at least \$20 and a few hours of time. I’ll come out ahead if I do nothing and put \$20 in my retirement plan and WAY ahead if I work 1 hour overtime, and put that in retirement as well.

Additionally, the carbon impact of manufacturing and shipping the transformer likely exceeds the 20 year savings.

Bottom line, this is not “low hanging fruit”. There are dozens of other things we can do that have a much bigger enviromental impact and cost savings per dollar/hour invested.

19. Jeff Carbine Says:

My favorite part of this article is the energy losses of a toroidal transformer are significantly lower than those of the preceding two EI-core transformers. Someone recently told me about this and it is different from what I understand. Thanks for helping me understand electrical transformers.

20. Derek Says:

After a long search I finally found a solid state high efficiency switching adapter that’s rated as Level VI. For those who want to save as much energy as you can, this is the way to go. Check out AirTech home automation for their 24v transformer. I also found a 16v, Level VI transformer from Trident that’s one sale at Amazon.